Studies are being performed which will identify the transcellular transport mechanisms for choline in various nephron segments. This requires the ability to measure choline in very small amounts. A choline kinase assay used in this laboratory has a sensitivity of 2-5 picomoles. The presence and activity of the enzyme, choline oxidase, in the rabbit kidney is being investigated. This enzyme plays an important role in the transcellular transport of choline. Since the nephron segments to be used will be from the rabbit kidney, knowledge of choline oxidase activity is necessary prior to perfusion of the tubules. Compounds, such as dimethylaminoethanol, which may interfere with the renal transport and metabolism of choline, are being investigated for these effects. A study of the renal metabolism and excretion of the methylamines, present at elevated levels in plasma from uremics, is being continued. Since these amines may contribute to toxic symptoms present in uremia, the manner in which they are excreted and their possible interconversion may reveal the reason for the elevated plasma levels. Studies on the effect of ethanol on choline and electrolyte excretion will be pursued in the isolated rat kidney. Besides choline, excretion and reabsorption of such ions as magnesium, zinc, sodium and potassium, with and without the presence of ethanol, will be evaluated.